General Packet Radio Service (GPRS) is a 2G mobile communication network based on packet switching, and its related standard is enacted by the European Telecommunication Standards Institute (ETST). When the 3G mobile communication network comes, the GPRS has been evolved into the Universal Mobile Telecommunication System Packet Switch (UMTS PS) domain. The network framework of the UMTS PS is shown in FIG. 1 and it comprises the following network elements:
a NodeB: offering air interface connection for a terminal;
a Radio Network Controller (RNC): mainly managing the radio resource and controlling the NodeB, wherein the combination of the NodeB and the RNC is called Radio Network System (RNS), and an Iub interface is used to connect the RNC and the NodeB, and the terminal accesses to the Packet Core of the UMTS through the RNS;
a Serving GPRS Support Node (SGSN): saving the information of the user's location in the routing area, taking charge of the security and access control, wherein the SGSN connects with the RNC through an Iu interface including an Iu-C interface and an Iu-U interface;
a Gateway GPRS Support Node (GGSN): distributing IP addresses to the terminals and taking charge of the gateway functions to access to the external network, and in the interior, connecting with the SGSN through a Gn-C interface and a Gn-U interface;
a Home Location Register: saving the contract data of the users and their current SGSN addresses;
a Packet Data Network: offering the packet-based service network to the users, and connecting with the GGSN through Gi interface.
There are two kinds of data transmitted in FIG. 1: user plane's data and signaling plane's data. The user plane is responsible for transmitting the service data of the users, while the signaling plane is mainly responsible for managing the user plane, including establishing, releasing and modifying the user plane. In a UMTS PS system, the user plane's path from the User Equipment (UE) to the PDN passes at least three network elements: RNC 4, SGSN 2 and GGSN 3. Correspondingly, there are two tunnels: the tunnel from the RNC to the SGSN and the tunnel from the SGSN to the GGSN, thus, it is called double tunnel scheme. Since both the two tunnels are based on GPRS Tunneling Protocol (GTP), they are called GTP-U tunnel.
With the general development of IP Multimedia Subsystem (IMS) service and the popularization of other multimedia services, the service requires better performance and shorter delay of the transmission layer. Therefore, the Third Generation Partnership Project (3GPP) organization is researching to peel the SGSN from the user plane's path to be the only network element of the signaling plane, and the user plane only includes one tunnel: the GTP-U tunnel directly from the RNC to the GGSN. This is called direct-tunnel scheme, and it is shown in FIG. 2.
Compared with the double-tunnel scheme, the data delay is relatively short in the direct-tunnel scheme since there is one node fewer in the user plane, thus it is more favorable to transmit the multimedia service. However, in certain cases, such as a user is roaming while needs to access to the belonged GGSN, the user plane needs to be lawfully intercepted in the SGSN, the user has intelligent service, and the GGSN does not support the direct-tunnel scheme, the double-tunnel scheme is still needed. The SGSN determines whether to use the direct-tunnel scheme or the double-tunnel scheme.
In the present double-tunnel scheme, when the GGSN receives the SGSN uplink user plane's packet, the packet will be discarded if the GGSN determines that the user plane is abnormal, and the user plane Error Indication message is returned to the SGSN. After the SGSN receives the message, it initiates a process of deactivating Packet Data Protocol (PDP) context to the UE. The process is shown in FIG. 3 and it comprises the following steps:
301, according to the saved GGSN address and tunnel number, the SGSN 2 sends an upstream packet to the GGSN 3;
302, the GGSN 3 receives the packet but can not find out the corresponding user plane's context, it returns the user plane Error Indication message to the SGSN 2;
303, after the SGSN 2 receives the message, it initiates a process of deactivating the PDP context to the UE 1.
When the SGSN receives a RNC uplink user plane's packet, the packet is discarded if the SGSN determines that the user plane is abnormal, and the user plane Error Indication message is returned to the RNC. After the RNC receives the message, it locally releases a Radio Access Bearer (RAB). The process is shown in FIG. 4 and it comprises the following steps:
401, according to the saved SGSN address and tunnel number, the RNC 4 sends the upstream packet to the SGSN 2;
402, the SGSN 2 receives the packet but can not find out the corresponding user plane's context, it returns the user plane Error Indication message to the RNC;
403, after the RNC 4 receives the message, it locally releases the RAB.
In the direct-tunnel scheme, there is no modification for the RNC and the GGSN. After a direct tunnel is established, if the RNC still thinks the Error Indication comes from the SGSN after it receives the Error Indication from the GGSN, it directly releases the RAB. Therefore, although the RNC has detected that the PDP context do not exist in the GGSN, it still can not timely notify the SGSN and the UE to release the PDP context, and the user can not receive the downstream data for a long time, which gives the user a bad experience.
The present invention offers a method in which RNC sends a notification message to the SGSN after the RNC detects that the GGSN is abnormal. After the SGSN receives the message, it initiates the process of deactivating the PDP context to the UE, thus ensuring the PDP contexts in the UE, the SGSN and the GGSN consistent.